1. Field of the Invention
The present invention relates to a novel alkoxysilyl group-containing azo compound usable as a radical generator having reactivity with silica and a metal oxide, a method for producing the azo compound, a rubber composition using the azo compound, and a pneumatic tire using the rubber composition.
2. Background Art
When silica is used in a rubber composition, various sulfur-containing silane coupling agents are used for the purpose of improving dispersion of silica. Performance of a rubber is influenced by a silane coupling agent added. Therefore, for example, a silane coupling agent capable of improving performance such as less heat build-up required in a tire is demanded.
A polymer having a functional group introduced in a molecular terminal is useful because the functional group can be used for a crosslinking reaction of the polymer and stabilization of dispersion of a filler such as silica particles. Particularly, in the case of a polymer having an alkoxysily group at a terminal, the polymer can be expected to form a crosslinking point by polycondensation and to act as a silane coupling agent that is hydrolyzed to react with a surface of an inorganic material such as silica particles.
Regarding the introduction of a terminal functional group in a polymer, for example, JP-A-8-104710 (1996) describes that alkoxysilanes having an isocyanate group are reacted with an azo compound having a functional group that reacts with the isocyanate group to form a macroazo radical initiator, and an alkoxysilyl group-terminated vinyl polymer is obtained using the radical initiator.
Japanese Patent No. 2510345 discloses an alkoxysilyl group-containing azo compound that can provide a novel polymerization method, as a radical polymerization initiator, and describes that the compound can be used in the same way as a silane coupling agent. A method for reacting an ester group or amide group-containing azo compound is reacted with an alkoxysilyl group-containing primary amine in the presence of a metal alkoxide catalyst is disclosed as a production method of the compound.
However, an isocyanate group and a metal alkoxide used in a production method of the above-described conventional technique have high reactivity with water, and therefore have the problem that synthesis conditions are strictly restricted in any of the production methods, and productivity is low. From the above facts, an alkoxysilyl group-containing azo compound does not yet result in practical use as a silane coupling agent.